Local area networks (LANs) allow organizations to share information over a high speed network that may be assembled with relatively inexpensive hardware components. LANs also provide for relatively inexpensive hardware connections to networks beyond the LAN by allowing multiple users within the LAN to connect to each of multiple networks outside of the LAN through an interface common to all users. Initially, LANs were limited to hardwired infrastructure, requiring the user to physically connect to the LAN via a wired connection. However, with the recent growth of wireless telephony and wireless messaging, wireless communications have also been applied to the realm of LANs, resulting in the development of wireless local area networks (WLANs).
In order for multiple remote units (RUs) to exchange data with a WLAN, each such RU must first associate with a WLAN access point (AP). Typically, this is performed by an active or passive scan of the WLAN. In an active scan, the RU initiates the establishment and configuration of a link by broadcasting a Probe Request. The Probe Request includes a Service Set Identifier (SSID) and capabilities and data rates supported by the RU. Upon receiving the Probe Request, the AP determines whether the SSID included in the Probe Request is the same as the SSID associated with the AP. When the SSIDs are the same, the AP responds to the Probe Request by transmitting a Probe Response back to the MS that includes the SSID associated with the AP. In response to receiving a Probe Response, the RU transmits an Association Request to the AP that includes the SSID and that further may include an indication of the time interval between each time the RU wakes up to listen for the AP (a ‘listener interval’). Upon receiving the Association Request, the AP transmits an Association Response to the RU that includes a status code (indicating that the association has been successful) and, in low power situations, an Association Identifier (AID) that is used to individually identify the RU for data delivery by the AP.
In a passive scan, instead of utilizing a Probe Request and a Probe Response, the RU listens for a Beacon that is intermittently transmitted the AP. Similar to the Probe Response, each Beacon includes the SSID associated with the AP and capabilities and data rates supported by the AP. If the RU likes what it sees in the Beacon, it may transmit an Association Request to that AP.
The presence of a large number of RUs in an AP's coverage area can lead to several problems. For example, the addressing range for AIDs is limited for each AP, which constrains the number of RUs that can be served. By way of another example, if a need arises to concurrently contact a large number of RUs, a very large Beacon may be needed to identify all of the RUs, that is, to identify the AIDs associated with all such RUs. Still another example is that if, in order to conserve power, each RU of the multiple RUs requests a large listen interval, the AP may require a very large buffer to individually hold data that may be intended for each of the multiple RUs. The AP may not accept a large listen interval and deny the association request. This would either require the RU to try a smaller listen interval value which would require a more active engagement or to be unable to connect to its control system.
Therefore a need exists for a method and apparatus that optimizes AID assignment by an AP, conserves RU power, and minimizes a required size of data storage buffers at AP.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.